Clinical and epidemiologic features of Rocky Mountain spotted fever in Mississippi, 1933-1973.

During the period 1933-1973, 169 cases of Rocky Mountain spotted fever (RMSF) were either reported by physicians or detected in a retrospective survey of hospitals and practicing physicians in Mississippi. The epidemiologic characteristics of 119 cases and the clinical features of 75 serologically confirmed cases are summarized in this communication and compared with other published reviews of RMSF. Although the percentage of reported fatal cases decreased overall since 1950, 9 of 49 reported cases (18%) in Mississippi were fatal during the period 1969-1972. The yearly number of reported cases of RMSF in Mississippi increased fourfold from 1970-1973. In the past 40 years, only 5 cases of RMSF have been reported from the Mississippi delta, a flat agricultural region that includes over one fourth of the total population of the state.